fix(flashcards): increase rotation sensitivity 10x for visible grab point physics

The previous scale factor of 5000 made rotation changes too subtle to see.
Reduced to 500 (10x more sensitive) so card rotation is clearly visible
when dragging from off-center grab points.

Also added detailed rotation logging during drag to help debug:
- Shows current rotation angle
- Shows rotation influence being applied
- Shows cross product value from physics calculation

This will help test and tune the rotation feel.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/components/InteractiveFlashcards.tsx

@@ -191,13 +191,21 @@ function DraggableCard({ card }: DraggableCardProps) {
     // If grabbed on left and dragged right → clockwise rotation
     // If grabbed on right and dragged left → counter-clockwise rotation
     const crossProduct = grabOffsetRef.current.x * deltaY - grabOffsetRef.current.y * deltaX
-    const rotationInfluence = crossProduct / 5000 // Scale factor for reasonable rotation (adjust as needed)
+    const rotationInfluence = crossProduct / 500 // Reduced scale factor for more visible rotation
     const newRotation = baseRotationRef.current + rotationInfluence
 
     // Clamp rotation to prevent excessive spinning
     const clampedRotation = Math.max(-45, Math.min(45, newRotation))
     setRotation(clampedRotation)
 
+    // Log rotation changes occasionally (same throttle as shadow logging)
+    const timeSinceLastLog = now - lastLogTimeRef.current
+    if (timeSinceLastLog > 200) {
+      console.log(
+        `[GrabPoint] Rotation: ${clampedRotation.toFixed(1)}° (influence: ${rotationInfluence.toFixed(1)}°, cross: ${crossProduct.toFixed(0)})`
+      )
+    }
+
     // Update card position
     setPosition({
       x: dragStartRef.current.cardX + deltaX,